This invention pertains to the solvent extraction of copper values using dihydroxy azoarenes as the extracting agent and more particularly to extraction of copper values from acidic aqueous solutions containing iron values.
Liquid ion exchange has been used as a separation process for removing metal ions of choice from an aqueous leach stream by utilizing an oil-soluble ligand having a particular affinity for that metal ion. The desired metal is subsequently stripped from the ligand in another operation. Liquid ion exchange, also referred to as solvent extraction, has been particularly successful in recovering copper from ores by leaching with a dilute aqueous acidic solution which is then extracted with a water immiscible solution containing a suitable ligand. The copper is next stripped from the ligand by strong sulfuric acid which concentrates the copper so that it can be recovered by electrolysis or other means known in the art.
Among the ligands which have been used in the past for the recovery of copper values are hydrocarbyl-substituted 8-hydroxy quinoline compounds, aminohydroxyalkyl compounds such as 9 (10)-amino-10 (9)-hydroxy stearonitrile, quinaldinic acids, hydroxy benzophenoximes such as 2-hydroxy-3'-methyl-5-ethylbenzophenoximes, bisphenol sulfides, mixtures of amines and carboxylic acids, and the like.
While many of these ligands have performed in an acceptable manner in the initial chelating operation, it is known in the art that it would be desirable to operate at temperatures higher than room temperature. The combination of these elevated temperatures and the highly acidic operating conditions encountered causes decomposition over a long period of time requiring replenishment. This replenishment causes the cost of extraction of the copper values to increase. There is, therefore, a continuing search in this industry for improved ligands which combine high extracting power with stability in use.
The leaching process wherein the copper ions are separated from the ore by dissolution in sulfuric acid also affects the dissolution of iron such that the final acidic solution usully contains a higher concentration of ferric ions. The solvent extractant, to be useful, must be able to selectively extract copper ions in the presence of a large excess of ferric ions.